Separation membrane modules can be classified into a spiral type, a plain membrane type, a hollow thread type, and others depending on the mode of a separation membrane unit, where, by permeating liquid or gas, components can be separated or concentrated. For example, a spiral-type membrane module generally has a structure such that a plurality of spiral-type membrane elements (hereafter also referred to as “membrane elements”) having a tubular shape are connected in series and installed into a pressure-resistant vessel (for example, see the patent document 1). This membrane element typically has a wound body of separation membrane units (hereafter referred to as “wound body”) and end surface holding members that hold the end surfaces thereof. Also, the aforesaid wound body has a structure such that a single or plural separation membrane unit including a separation membrane, a supply side flow path material, and a permeation side flow path material are wound around a perforated hollow central pipe.
FIG. 5 is a cross-sectional view of an essential part illustrating an element connection part of a conventional spiral-type membrane module. As shown in this Figure, an end surface holding member 36 is disposed on the end surface of a wound body 32. Also, an FRP (outer cladding material) 31 is wound around the outside of the wound body 32 and the end surface holding member 36. Further, by curing this FRP 31, the FRP 31 is integrated with the wound body 32 and the end surface holding member 36.
A hub plate 36a is disposed in the end surface holding member 36. In actually performing fluid separation, a force deriving from the pressure difference between the supply side and the concentration side of the apparatus acts in a direction from the supply side to the concentration side of the membrane element. This force is supported by the end surface holding member 36 disposed on the concentration side. This prevents telescopic phenomenon of the wound body 32 from occurring. Also, in the outer circumferential part of the end surface holding member 36, a groove 36b that extends in the circumferential direction thereof is disposed. Further, an annular sealing member 37 is mounted in one of the grooves 36b of end surface holding members 36 adjacent to each other. This annular sealing member 37 seals the gap between a pressure-resistant vessel 38 and the FRP 31.
In connecting the membrane elements with each other in series, the two are connected by inserting and innerly fitting a connection pipe 34 into a central pipe 33 in the case of FIG. 5. An annular groove 39 is disposed on the outer circumferential surface near the both ends of the connection pipe 34, and an O-ring 35 is mounted in this groove 39.
In the aforesaid conventional spiral-type membrane module, the membrane elements are not fixed to each other, so that, at the time of starting and stopping the operation, relative displacement occurs mutually in the axial direction, and the O-ring 35 is liable to slide on the inner surface of the central pipe 33. This generates abrasion of the O-ring 35, whereby leakage occurs from the supply side to the permeation side, raising a fear that the water quality may be degraded.
In order to solve such problems, the following patent documents 2 to 4 exemplify a connection member for fixing the membrane elements with each other. However, none of these connection members discloses a constitution of the present invention, and raises a problem such that the work of connecting the membrane elements is cumbersome or the structure is complex.
On the other hand, in accordance with an increase in the scale of membrane processing plants, reduction of the area for disposing a membrane separation apparatus is demanded. Conventionally, use of a membrane element having a diameter of 8 inches (about 200 mm) was prevalent. However, due to the above demand, reduction of the number of membrane elements is desired and, for that purpose, a measure of increasing the membrane area per one membrane element has been progressively taken by increasing the diameter of the membrane element.    Patent Document 1: Japanese Patent Application Laid-open No. 11-267469    Patent Document 2: Translation of PCT Application No. 2007-517661    Patent Document 3: Translation of PCT Application No. 2004-536703    Patent Document 4: Japanese Patent Application Laid-open No. 2007-190547